Washington -LRB- CNN -RRB- -- If the threat of underwear bombs became known last Christmas , why did airport screeners only recently begin aggressively checking for them ?

The answer is two-fold , Transportation Security Administration Director John Pistole told reporters Tuesday . First , the lack of a permanent leader at the TSA hindered change , he said . Secondly , the agency needed time to train screeners on the new pat-down protocols .

The threat of hidden bombs became instantly clear on December 25 , 2009 , Pistole said , when authorities arrested Umar Farouk AbdulMutallab , a Nigerian man , after his failed attempt to ignite his hidden explosive on a flight from Amsterdam to Detroit , Michigan . TSA officials immediately started looking at what they needed to do to modify technology or pat downs to detect the bombs , he said .

But at that time , the top job at TSA was filled by a career official . The White House delayed nominating a TSA chief and then White House and Congressional Republicans feuded for a year over nominees . Much of the debate centered on whether the nominees supported unionization of airport screeners . Two of President Obama 's nominees withdrew from consideration .

`` Frankly it just came down to the fact there was not a presidentially appointed , Senate-confirmed administrator in place until I was confirmed at the end of June to make a really significant decision like that , that would have impact on a number of people , '' Pistole said . `` That was a big part of it . ''

Pistole was sworn in as administrator in July and soon thereafter made the decision to go through `` enhanced pat downs . '' Training time accounts for the rest of the delay , as the TSA quietly began pilot programs in Boston , Massachusetts , and Las Vegas , Nevada , in August , and rolled the program out nationwide in early November .

Pistole consistently has said it was his decision to implement enhanced pat downs . He said he opted not to publicize them in advance because he felt to do so would be to give a `` roadmap '' to would-be terrorists .

Implementation of the pat downs was further delayed because time was needed to train screeners on the new protocols , he said .

Those protocols are considered sensitive security information , and have not been shared with the public .

But Pistole said protocols do not allow for screeners to grope passengers .

Pistole said some passenger descriptions of the procedures are `` so wildly outside the standard operating protocols that it just absolutely should not be happening . If it is , then we 'll take appropriate action . ''

`` If we receive any complaints from a passenger about something happening , then we immediately follow up both with that passenger and with our security officers , '' he said .

Most airport checkpoints have closed circuit television systems , which help investigators find out what happened , he said .

Videotape helped dispel one passenger 's complaint that she was handcuffed to a chair and mistreated , he said .

`` If there 's a security officer that did something that 's not appropriate , then we take appropriate action . I just want to make sure that I have all the facts , '' Pistole said .

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The failed underwear bombing last Christmas raised the threat of bombs hidden in clothes

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Pistole says after that , the pat-down program was delayed by two factors

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The TSA lacked a permanent leader until July

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Extensive training also was required before implementation of the program , he says